When are U.S. forces in Afghanistan allowed to shoot back when they come under attack? An episode last month illustrates the quandary American troops face. In early June, on the southern edge of Kandahar city, a small Army convoy drove into a nighttime ambush. Within seconds, a turret gunner in one of the vehicles was hit in the arm. Muzzle flashes pierced the dark, alerting fellow troops to where the shots were coming from. But, thinking that they had to clearly identify the triggerman before firing back, they waited before retaliating, even as rounds of hostile fire poured in. Only after an officer radioed back with the go-ahead did the Americans return heavy fire. By then, the militants had melted away.

The wounded soldier, Private First Class Trevor Longcore, of Shadow Troop, 1-71 Cavalry, caught a lucky break: he wasn't hit by a bullet but by a piece of shrapnel that had apparently ricocheted off his vehicle's armor. But a month into their deployment into Afghanistan, he and his compatriots are still frustrated by the constant heat-of-the-moment uncertainty about returning fire. For many troops, the strict rules of engagement  overlaid with tactical directives meant to limit civilian casualties  are a source of confusion and, they contend, are putting U.S. soldiers in greater danger. "We have all of these stupid rules that in the end wind up hurting more people. I mean, hesitation can mean death out here," says one disgruntled soldier serving in the volatile south. (See pictures of the U.S. Marines' offensive in Afghanistan.)

Afghanistan has never been more dangerous for foreign troops. In June, 102 were killed across the country, more than half of them Americans, making it the deadliest month since the war began in late 2001. General Stanley McChrystal, the ousted commander of international forces, forecast the scenario last summer when he tightened the use of airpower, artillery and lethal force in population centers. Increased risk to U.S. forces and more military casualties, he said, were the price of a counterinsurgency strategy that requires more boots on the ground to win over war-weary Afghans in Taliban strongholds. Now that he has been replaced by General David Petraeus, some hope the rules of engagement will be eased. In a Sunday memo to troops, he affirmed that "protecting those we are here to help nonetheless does require killing, capturing or turning the insurgents. We will not shrink from that." (See pictures of the rise and fall of General Stanley McChrystal.)

It's not clear, though, what changes will take place. Petraeus has said flat out that he will not change the counterinsurgency strategy set in motion by his predecessor. While downplaying changes to the rules of engagement, he has nevertheless pledged a "hard" review to ensure they are implemented more evenly and efficiently across the battlefield. Indeed, some coalition officers grumble that tactics used in one area, like night raids on suspected militant hideouts, are widely viewed as forbidden elsewhere in the wake of reports of civilian deaths. These vagaries about allowable operations, they say, need to be cleared up. The same goes for the parameters that will make it appropriate to engage enemy fighters  the situation that stymied the Americans in the June incident in Kandahar.

Army Colonel Wayne Sparks, a spokesman for coalition forces, says the problem is largely one of "perception" between standing NATO rules of engagement that have never changed and McChrystal's directives issued as guidance to units downrange. The rules are long established, he explains, but they have been colored by a series of directives aimed at protecting civilians, which may have led to some misinterpretation in the ranks. Analysts say that Petraeus may move to clarify these distinctions. Yet given that he was the author of the U.S. counterinsurgency manual that informed much of McChrystal's strategy, they are reluctant to predict any major departures. This could spell disappointment for those on the front lines of the war who want clarity. (See Joe Klein on the Obama and Petraeus partnership.)

In Marjah, the desert town in central Helmand province where U.S. Marines are battling a resurgent Taliban, roving groups of militants on foot and motorbike take potshots at the Americans when they are not setting up ambushes and IEDs. Yet even if Marines see an attack taking shape around them, the current rules of engagement mandate that they cannot shoot unless they are first shot at. The insurgents know this, so they often "drop and go": firing from a distance, then abandoning their weapons. Sometimes Marines never get a single shot off in defense, an exercise in restraint that is especially taxing for the American military's hardiest warriors. "It's hard as hell holding back when you know what's coming every time," says a lance corporal from Lima Company, Third Battalion, Sixth Marines. It's a commonly held grievance, but as usual the Marines make do. Staff Sergeant Christopher Whitman, a platoon leader, argues that discipline is the only way to avoid the big mistakes that forfeit the support of the traditionally xenophobic locals, difficult as it may be at times. Says Whitman: "[The Taliban's] will to fight may be as strong as ours. But it's our duty to keep ours measured."

This story was reported with a grant from the Pulitzer Center on Crisis Reporting.